/// <reference name="MicrosoftAjax.js"/>
    
    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);
                
    function EndRequestHandler(sender, args)
    {
       if (args.get_error() != undefined && args.get_error().httpStatusCode == '500')
       {
           var errorMessage = args.get_error().message
           args.set_errorHandled(true);
           alert("The following error message occured during the processing of this page:\n" + errorMessage );
       }

    }